Wednesday, November 30, 2011

TEPCO's worst-case scenario (here and here) pales in comparison with the analysis by the Institute of Applied Energy, also presented on November 30 at the workshop held by the Nuclear and Industrial Safety Agency.

The analysis done by the Institute of Applied Energy commissioned by the national government, 85% of fuel dropped to the Containment Vessel in Reactor 1, and 70% of fuel dropped to the Containment Vessels in Reactors 2 and 3. The researchers at the Institute pointed out the possibility of the damage to the stainless-steel shroud that surrounds the fuel core, and of the corium having eaten away the concrete floor of the Containment Vessel up to 2 meters deep. Because of that, they also said it was possible that the RPV got tilted.

Yomiuri doesn't specify which Reactor the Institute of Applied Energy was talking about, but my guess is Reactor 1.

Some nuclear experts have suggested that if the corium had escaped from the RPV it would spread out flat and evenly on the pedestal and be easily cooled by water. Well, even TEPCO admits that may not the case as far as the shape and the location of the corium is concerned (they do say the corium is cooled), and the Institute of Applied Energy says the corium could be 2 meters deep into the concrete.

My totally amateur 2 cents are that the concrete foundation may have cracked in the earthquake, and that it is possible that the crack or cracks are there in the pedestal. So, even if the corium wanted to spread out thin and flat, it would find those cracks and go there. Once the core-concrete reaction starts, it would be a positive feedback loop; the temperature gets higher not just from the contact with the corium but from the core-concrete reaction, the hole in the concrete would get bigger, and more corium would go into the bigger hole.

(From my other post on the topic, TEPCO's drawings indicating the thickness of the CV concrete)

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comments:

Little by little the truth comes out so as not to shock and enrage the sheeple, but to slowly let the sheeple deceive themselves that its not that bad, until the "acceptance" part of the loss comes in.

If it's in the cement, then the corium cannot be effectively cooled and will eventually, sooner rather than later, melt into a critical explosion in the water table. By this time the Russians were already building a containment wall below the reactor. TEPCO on the other hand ain't doin' jack $hit.

Also keep in mind that steel melts around 2500 deg F, Corium fissions at around 5000 deg F “Blob temperature”. The cute little “blob” that TEPCO showed in their recent drawing of a Corium out of the box was deceptive in size, the real mass of the Corium will be !!!! 200 TONS !!!! of fissioning, poisonous, super hot hell on earth. Y’all TEPCO boyz got a 200 ton blob of stuff and you can’t tell me where it is?

The sheer stubbornness of the TEPCO people is stunning. Do they really believe that if they ignore the extreme danger of this it will just go away? It is bad enough that they are willing to sacrifice their own people but the dispersal of long half life radioactive elements will harm all life all over the planet. It is beyond being unbelievable. What is wrong with them?

the China Syndrome: from the notion that the molten reactor contents could hypothetically sink through the earth to reach ChinaFirst Known Use: 1970 http://www.merriam-webster.com/dictionary/china+syndrome

The idea that the molten fuel would melt the earth's crust, let alone reach China, is obviously nonsense, intended as a joke. From Wikipedia.

The corium may not melt it's way to the center of the earth, but it certainly isn't going to stay put. I also think the pedestal is cracked-between the earthquake, tsunami, and explosions, how can it not be? Why would TEPCO build the pedestal to a higher standard than the rest of the plant? That would cost too much.

"Once the core-concrete reaction starts, it would be a positive feedback loop; the temperature gets higher not just from the contact with the corium but from the core-concrete reaction"

The core-concrete reaction *consumes* energy, meaning the temperature gets lower, not higher. It's like throwing a red glowing hot iron into the water - lots of violent water vapor gets released, but the iron does get cooler. Same with corium (but the problem of course is, the corium constantly heats itself).

It's a sad state of affairs that the "China Syndrome" sci-fi movie seems to be the main source of education about chemistry, physics and nuclear power.

Several reactions occur between the concrete and the corium melt. Free and chemically bound water is released from the concrete as steam. Calcium carbonate is decomposed, producing carbon dioxide and calcium oxide. Water and carbon dioxide penetrate the corium mass, exothermically oxidizing the nonoxidized metals present in it and yielding gaseous hydrogen and carbon monoxide; large amounts of hydrogen can be produced. The calcium oxide, silica, and silicates melt and are mixed into the corium. The oxide phase, in which the nonvolatile fission products are concentrated, can stabilize at temperatures of 1300–1500 °C for a considerable time. An eventually present layer of more dense molten metal, containing fewer radioisotopes (Ru, Tc, Pd, etc., initially composed of molten zircaloy, iron, chromium, nickel, manganese, silver, and other construction materials and metallic fission products, and tellurium bound as zirconium telluride) than the oxide layer (which concentrates Sr, Ba, La, Sb, Sn, Nb, Mo, etc. and is initially composed primarily of zirconium dioxide and uranium dioxide, possibly with iron oxide and boron oxides), can form an interface between the oxides and the concrete below, slowing down the corium penetration and solidifying within a couple of hours. The oxide layer produces heat primarily by decay heat, while the principal heat source in the metal layer is exothermic reaction with water released from the concrete. Decomposition of concrete and volatilization of the alkali metal compounds consumes substantial amount of heat.[2] The fast erosion phase of the concrete basemat lasts for about an hour and progresses into about one meter depth, then slows to several centimeters per hour, and stops completely when the melt cools below the decomposition temperature of concrete (about 1100 °C). Complete melt-through can occur in several days even through several meters of concrete; the corium then penetrates several meters into the underlying soil, spreads around, cools and solidifies.[3] During the interaction between corium and concrete, very high temperatures can be achieved. Less volatile aerosols of Ba, Ce, La, Sr, and other fission products are formed during this phase and introduced into the containment building at time when most of early aerosols is already deposited. Tellurium is released with progress of zirconium telluride decomposition. Bubbles of gas flowing through the melt promote aerosol formation.[2]

"The oxide layer produces heat primarily by decay heat, while the principal heat source in the metal layer is exothermic reaction with water released from the concrete. Decomposition of concrete and volatilization of the alkali metal compounds consumes substantial amount of heat.[2]"

So what is it? Are we dead yet or is it impossible for the melted fuel to eat its way through 10 meters of concrete?

Your amateur analysis of the migration potential is spot on. As a MSME material scientist from U of Michigan, easily a crack propogated during earthquake, or a normal pre-engineered expansion crack could easily provide a path to accelerated bypass of the containment.

Personally I think the corium is beneath the buildings completely. Remember the "steam from the ground" from months ago?

The "steam from the ground" was actually detected in the first floor of the reactor building. Some Japanese blogger quoted the mail of a worker at the plant which was talking about steam inside the buildings, the blogger took part of the mail out of context implying that the cracks were appearing all over the perimeter of the plant, some retards translated it without paying attention to the original source and it ended up in Russia Today as a proof of the China syndrome. Arnie Gundersen already said that there was no data confirming anything like that.

In the first few days of the quake a five inch wide crack was discovered running the length of the outside parking lot, so deep that when a worker accompanied television crew shined a camera down into it, it showed no bottom. There is very little chance that after a quake and tsunami of such magnitude that whatever 'pedestal' is underneath is not fractured with multiple-sized cracks and probably even tilted, if not busted every which way from Kansas with a large single crack that completely compromised the concrete portion of the containment from Day 1. From what I saw it appeared as if a whole shelf of the land slid towards the sea right across all six reactors, very well contributing to the subsequent explosions and outgassing. Also, the roof on one of the buildings appeared to have been partially swept over top by the tsunami as it quite possibly elevated from being squeezed in-between the buildings, an incredible feat indicating the enormity of what transpired. I really think the cores and spent fuel rods are long migrated under and away, and a geological topography of the location with commentary on water table interaction would be appreciated. Discussion of the reactor buildings appears to be a distraction at this late date and given the original estimate of some two years to cool off all the spent fuel rods stored on site, then that part is still very much in play at the 8 month hash mark. E.

@Atomfritz, that's from June, man. And, as I said, it's inside the reactor building, not around the perimeter of the plant, like it was implied a couple of months later in Russia Today (the other end of the broken telephone): http://www.youtube.com/watch?v=baya8-agPs4

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